1. Field of the Invention
The present invention relates to a method of grinding a semiconductor wafer having bumps formed on one surface, particularly grinding the bump-free surface of the semiconductor wafer so that the wafer may be reduced to a predetermined thickness.
2. Related Arts
Referring to FIG. 8, a plurality of chips or pellets each having an integrated circuit pattern formed thereon can be provided by cutting a semiconductor wafer W along crosswise streets S to separate it into small squares. Prior to dicing the rear surface of the semiconductor wafer is ground a predetermined thickness to reduce its heat storage capacity. Also, this meets the downsizing requirement.
Referring to FIG. 9, the front surface 61 of the semiconductor wafer W is laid and sucked onto the chuck table 62 of a grinder, and a rotary whetstone 63 is applied to the rear surface 60 of the semiconductor wafer W under a predetermined pressure.
The grinding can be equally effected no matter which type of semiconductor pellets may be, pellets to be packaged for surface-mounting such as chip size packages (CSPs) or ball grid arrays (BGAs) or bare chips to be mounted on printed-wiring boards.
Such pellets P, however, have bumps formed thereon for making required connections to selected electrodes in printed-wiring boards. The semiconductor wafer W is ground while being laid on the chuck table 62 with its rear, bump-free surface up. As the semiconductor wafer W is pushed against the chuck table 62, it is liable to be broken by the stress, which will be caused by the bumps as a counter force to the push given to the semiconductor wafer W by the rotary whetstone 63.
In an attempt to prevent the semiconductor wafer from being broken an adhesive tape 64 is applied to the front surface of the semiconductor wafer W, thereby allowing the bumps to be buried in the thickness of adhesive layer, as seen from FIG. 10. The adverse effect, however, cannot be reduced completely with recourse to this remedy, and what is worse is that: adhesive agent is apt to remain more or less on the semiconductor wafer W after removal of the tape 64 from the semiconductor wafer, thus lowering the quality of pellets significantly.
After bonding the bumps of a pellet to selected electrodes of a printed-wiring board the space between the printed board and the pellet is usually filled with resin, thereby solidifying the pellet-and-printed board combination. To assure that a good electric connection be established between each bump and the counter electrode it is necessary that the bump is 0.09 mm tall, but to reduce substantially the possibility of the semiconductor wafer being broken it is necessary that the bump is 0.05 or less tall. Disadvantageously this necessity is a cause for incomplete bonding between bumps and electrodes, leading to disconnection between the printed circuit and pellets.